Artificial superlattices with abrupt interfaces by monolayer-controlled growth kinetics during magnetron sputter epitaxy, case of hexagonal CrB2/TiB2 heterostructures

• Monolayer-controlled growth kinetics during interface formation. • Superlattices with abrupt interfaces by magnetron sputter epitaxy. • Refractory CrB 2 /TiB 2 diboride superlattices suitable for neutron mirrors. • 1-µm-thick superlattices without accumulated roughness. • Average interface widths of 1–2 unit cells for different modulation periods. Artificial superlattices exhibit exceptional electronic, magnetic, optical, and mechanical properties which make them unique candidates for applications in a broad range of technologies. A common key feature of superlattices is the need for atomically abrupt interfaces. However, superlattices comprised of materials with different properties, such as melting points and diffusivities, pose large challenges for achieving high crystal quality of both constituents with abrupt interfaces. By employing ion-assisted magnetron sputter epitaxy, we present an innovative solution to this problem with utilizing a unique combination of thermal radiation and kinetic energy that enable sufficient adatom mobility for epitaxial growth of both materials. The research was implemented for the case of CrB 2 /TiB 2 heteroepitaxial superlattices, as neutron interference mirrors, wherein the constituents’ melting points differ by 1100 K. Ion-induced intermixing was avoided by commencing growth of each TiB 2 and CrB 2 layer by up to 3 unit cells (uc) without ion assistance, forming a buffer to protect the interface during the ion-assisted growth of the remainder of each layer. Heteroepitaxial superlattice growth with interface widths σ CrB2 ∼1 uc and σ TiB2 ∼2 uc was confirmed for different modulation periods. More than 3000 uc (∼1 µm) thick superlattices with abrupt interfaces were demonstrated for neutron mirror applications.